Extractive distillation of hydrocarbons with furfural-water mixtures



2,419,039 WITH V. SCARTH FURFURAL-WATER MIXTURES Filed Dec. 2l, 1944 EXTACTIVE DISTILLATION OF HYDROCARBONS April 15, 1947.

INVENTOR Vl RGH. SCARTH E" @4m a ATTORNEYS Numdam rural as the solvent.

' Waller.

Patented Apr. 15, 1947.

EXTRAC-TIVE DISTILLATION OF HYDRO-j CARBON S `WI1`H FURFURAL-WATER MIXTURES Virgil Scarth,l Bartlesville, Okla., assg'nor to Phillips 'Petroleum Company,r a corporation of Delaware Application December 21, 1944,v Serial No. 569,244

9 Claims. (c1. 19e-rs.)

This .invention relates to the extractive distillation of unsaturated hydrocarbons with furf-ural as the solvent, particularly to the extractiva distillation of hydrocarbon streams containing alphatic olens and/or conjugated diolens, yespecially normal butene and/or butadiene, to recover same therefrom.

It `has become Acustomary lto recover unsaturated hydrocarbons particularly normal butene and/or butadiene from hydrocarbon streams containing same by extractive distillation with fur.-

Such lprocesses are described in the patent to Hachmuth .2,386,31vv'and inthe copending applications of .Hachmuth, Ser. No. 438,844, led April 13, 1942, and Ser. No. 454,312, filed August l0, 1942. VThe rst-mentioned application discloses .and claims the use of furfu-ral containing several per cent of dissolved It will not be necessary to describe the extractive Adistillation process Yin detail .since it is now qui-te Well-known to vthe art. Suffice fitto say that it is carried out by means of a fractional distillation column operated as an absorber into the top of which a stream of iuriural is vcontinuously fed, the ,rich -f-urfuralwithdrawn as bottom product being passed to .a strpperscolumfl Where the dissolved bu-tene and/or butadiene. .is driven oft..v The lean iu-rfural is withdrawn from the bot. tom -of Vthe stripper, cooled, and recycled, to :the absorber. Both absorber and-stripper Vare refluxed by means :of a portion of condensed overhead andboth are provided with reboilers.

During the,r absorption and .st-ripping, operations polymer land other corrosive impurities are formed vin the iurfural and .build .upto an objectionable'e-xten-t so that `it is necessary to ,Fa-ss. a

sidestream `of -therfuriural to a reeru-n unit Where it is freed from thepolymer and otherimpui-ities, usually by 'aprocessinvolving .steam-fdistillation. Methods otre-.running the furiural .are `4 disclosed in the .patents tto Buell et alg. 2 5.0,58.4, Hachmuth 2,350,609, and Hac-hmuth 2,312,668..

There-running operation as-comr-neroially practicedzgives an overhead of steamand pureiurfullal which upon condensation gives a Waterlayer .and a puriiied furfural layer. The waterlayeris used to ymake .steam employed inthe steam distillation for re-ru-nn-i-ng the -iurfu-:aL Waterlayer is saturated Withfurfural (about-8,7%Aat 120" E.) This .dissolved iurfural has gin .the-pastbeen saved by using the water layer to make. the proef essr steam used the 11e-run operation. However, in making steam by' this method the tubesy in the. steam generator -haverbeen .dimcult tor .keepclean because iurfural dissolved in the Water becomes polymerized and deposits on the tubes..

In the kextraetive distillation of unsaturated. hydrocarbons ivi-th furiural containing dissolved water as arsolventywater 1is volatili/'Led and. `car-- red overheadn adm-fixture ywith the .hydrocarbon vapor. Upon condensation of the overhead vapors this Wateris condensed and forms a separate Water layer inthe reflux accumulator. This occurs inconnection with. both thel absorber and the stripper. Conventional practice in the past has been to add the-Watervthus stripped from theiurfural back to the iurfural. red to the absorber,

as; makeup Water.

It has been .commonly observed. that evenY when the. furiural in the extractiva distillation system reerun. at ,a ratesuchxas to rre-run all the furrural'.V inthe -system .every two orv three dayathe furiural :in the mainsystem,A i. e., the: extraotive distillation system proper., becomes corrosive.- This'corrosiveness is. objectionable because the equipment. such as the expensive'bubble- :tray abi sorber .and :stripper is eaten away at an excessive rate.. The causes underlying .the corrosivity oiE thel furiural are .not understood. at present.. Some investigators believe: that the. corrosiveness reesults from the decomposition and poiymerization of the furfural under .the .particular conditions prevailing in the absorber and; stripper with. .the formation .oi-:organic acids and. tortura-lf polymerwhi'clr ,are helievedl to be corrosive .of vcarbon steel. It; is thought. that other' factors areY involved since; corrosioni's. not alwaysl directly .proe portional to acid.l content of the'v furfural,` especial'ly at acid. levels above per. cent Weight measured as" acetic acid. For example, while: cor rosionisneyer serious; at: acidities;y below 0,194 per cent,- at. acidities.- between 05.04! :and A0.06g per 'centi serious-corrosion .may or mayy not occur dependa-` ing upon; .factors unknowrrat; present; and .att aciditiesaboye. 0.106I per .cent seri'ousiv corrosion. ise usually encountered and in some cases'itlissoex c essive` that the plant .l could be continued. operationior only ia, short period oi time before; it would be eaten awayftoafn-unsafe point; ltvcan. be. definitely stated that thef problem .ofl corrosion' ,byzfurfural lis most -diilicult to solve. at the: presen-trstateof thefarl. In fact, Soifar asl am aware; nov completelyv .satisfactory 'In-ethnols,` of completely eliminating` thefprob'lem- .oiv corrosion by furfural have; been .olevelopecl.4

Another;.disadvantage of present. methods of. operation`- is that the furfural becomes` corrosivo in the :extractiva distillation system and causesy corrosion vin v,the system beforeritgcan: reach the re run. unit since it'A is; necessary that! the.tunfuralE ref-run vrate be; kept. atY a minirrmmV because losses oiA furfurral. in theyre-run unitarehigh..

Theprincipal object` of thepresent' inventionxis; to provide an improved process of carryirrgout the extractive distillation' of` unsaturated. hydrocarbonsE with iurfural as the solvent. ,Another objectI iste-,provide such a. procession there-f covery: of normal ybi1- tene andyor butadiene.

corrosion of' the extractive .distillation ,system is;

substantially reduced. Another object is Vto provide such a process wherein the steam vaporizer or generator used for generating process steam for use in the furfural re-run unit is caused to` operate much more satisfactorily than 'when using present methods of operation. Another obj ject is to eliminate polymerization of furfural in the process steam generator with resulting deposition of objectionable material on the tubes of the vaporizer. method which accomplishes the foregoing aims and objects in a simple and economical. manner and which can be applied to existing furfuralextractive distillation systems, heretofore operated in the conventional manner, with a minimum of trouble and changes. Many other objects of the present invention will be apparent from the following description to those skilled in the art.

The accompanying drawing portrays diagrammatically an arrangement of equipment for carrying out the present invention. i I I While in the drawing I have shown only a single absorber and a single stripper it will be obvious thatany number of these may be employed. For example, in the manufacture of butadiene by the two-stage catalytic dehydrogenat-ion of normal butane it is now conventional to provide a furfural extractive distillation system for recovering unsaturated components from` each catalytic eiilu ent, the furfural extraction provided between stages serving to separate butene-Z from normal butane and the furfural-extraction operating on the second stage effluent serving to separate butadiene and butene-2 from other C4 hydrocarbons; it is customary to cool and combine the lean furfural streams leaving the bottoms of both strippers and to pass the resulting composite recycle stream to a common furfural surge or storage tank from which furfural is pumped to the absorbers;

it is also conventional to employ a single furfural re-run unit to which a sidestream of the lean furfural is' fed, the re-run furfural being merged with the recycle furfural passed to surge. In accordance with the present invention the water removed overhead in the absorber and stripper units of the extractive distillation system forming a separate layer in the overhead accumulator associated with the absorber and stripper is separately withdrawn and is employed as the sourceof steam employed in the re-running of thefurfural;

i I have discovered that the water which goes overhead in the absorberl and stripper units is corrosive. This Water contains up to about 1% of dissolved furfural (which is vaporized in the absorber and stripper in spite of measures taken to preventloss of furfural in this manner) and practically no inorganic chemicals. As explained above, past practice has been to add this Water as makeup to the lean furfural fed to the absorber in order to keep the level of dissolved water in the furfural substantially constant. The water recovered fromthe overhead was saved and added back to the extractive distillation system in order to conserve the furfural dissolved in the Water since Afurfural is very expensive and because at times it has appeared that the `available supply of furfural might be insuiiicient for the butadiene program. A

The nature of the corrosive material present in the water phase which appears in the condensate accumulators associated with the furfural absorber and stripper is not known nor is it known how it forms or why lit 4goes overheadvwith the water and hydrocarbon. The corrosive materiali Another object is to provide a' amaca@ A sorber and stripper.

' rosive material is removed as a vapor at the temperatures maintained in the absorber and strip- 4 probably forms in the absorber and stripper and is probably stripped from the furfural inthe ab- It is believed that the corper and that the concentration of this foreign material builds up in the Water if the water is continually returned to the furfural as make-up Water. When this water is added to non-corrosive furfural it becomes corrosive. Thus, when the water phase is added back to the system in accordance with existing practice the corrosive material is returned thereto.

I/have discovered that this difliculty can be overcome by employing the water layer as a source of process steam for the re-run operation. The Water may be fed to the conventional steam generator used for making the process steam and thereby vaporized, the resulting steam being injected into the re-run unit for steam distilling, the furfural being re-run. Alternatively the water may be introduced as liquid water into the rerun unit and vaporized therein by extraneous heat.

By passing the water layer, either as steam or liquid, to the re-run unit in accordance with the present invention, the corrosive substance; whatever it is, removed from the water. At the same time the furfural content of the water layer is conserved. Y

While it is preferred to eifect the distillation of the water in the re-run unit in the manner discussed above and described in detail below, the' distillation may be conducted in other Ways: for example, the water layer may be passed to a distillation unit and there distilled at atmospheric pressure whereby the corrosive material is caused to remain in the residue or kettle product. Such a plain distillation is ordinarily carried out in such manner that not over of the water appears in the distillate since upon concentration ofthe corrosive material beyond this point there is danger of driving corrosive material overhead. The distillation should not be carried beyond the point Where the kettle temperature exceeds the boiling point of water by one degree Fahrenheit.

The re-run operation may be carried out in the manner shown in Buell et al. 2,350,584, except that (1)I the water vlayer formed by condensing the furfural-Water overhead vapors is not passed to the steam vaporizer of the re-run unit but instead is passed to the extractive distillation system, for

example, being introduced as makeup to the lean furfural fed to the absorber in such amount as to maintain the content ofdissolved Water in the furfural solvent in the extractive distillation system at a substantially constant predetermined level, and (2) the steam vaporizer of the re-run unit is fed with the water recovered as a separate phase in the condensate accumulator employed for collecting the condensed overhead vapors from the absorber and stripper. The re-running operation is carried out at pressures ranging from atmospheric to moderately superatmospheric, say up to about 30 pounds gage, in order to minimize additional polymerization in the rerun step. Where straight distillation of the water phase in a unit apart from the re-run is practiced, pressures of the same order are employed.

The Water distillate resulting from distillation of the corrosive water phase in accordance with the present invention may be introduced tothe extractive distillation system, generally by addition as makeuprwater to the lean furfural fed to an -absorber unit inV the'system. Where, in accordance with the preferred practice of the finven'tion, the corrosive water Vphase is passed to the re-run unit and there vaporized to form steam, the water thereby vaporized ultimately appears as the water layer in the accumulator for the-condensed overhead vapors of the re-run-unit. This w'ate'r layer is free of corrosive material but is saturated with turfural and is preferably added -to the lean furfural fedto the absorber in Suchproportioiis as to impart the proper water level thereto. In this way the dissolved iuriur'al con* tent of the water layer is saved.

Wherey 'a re-rununit of the type shown in 2 'of Buell et al. 2,350,584, is' employed, I A#may introduce a portion of the corrosive water phase in-lidid form Vdirectly into one o the evaporators which are placed in series-ahead of the nalstripper into which process steam from the vaporizer is introduced. The evaporators are at such a high temperature that :suchliquid water is immediately .flashedinto steam therein. This pro'cedure gives ian exception-allypure re-run .furfurar practically water-white ira-color, and .in addition keeping the'temperature in the evaporators at va suitably 'low level. t is preferred to .iniect the .liquid water vinto the vsecond evaporator fo'f the series', although it mig-ht be introduced into the first evaporator. When the water is fed into the 'second evaporator in this 'manner it is vapori-Zed therein and passes in vapor phase through the rs't evaporator to vappear `:in the condensate settler.

The corrosive material contained in the corrosive water phase introduced to there-run vunit in accordance with thepresentinvention is eliminated along with the' polymer from lthe .nal stripper column in the re-run unit. Likewise, where the water phase `ifsrsultec'ted to simple distillation to remove non-"corrosive water as an overhead Iproduct the residue vcontaining the corrosive material .is withdrawn Vfrom the still or column and discarded.

My invention takes advantage fof Vtwo unexpected discoveries; lrst, that corrosive material fi's volatifle and removed overhead from `the ur- 4farai absorber :and .stripper under the conditions of operation and. concentrated .in the water layer separating in the overhead accumulatore, and, second, that this corrosive material vcan be removed from the water by distillation preferably byv vaporizing "the'water phase Sand injecting the resulting steam into the reerun unit and/or injecting at V.least a portion of the water phase directly into 'the ire-run unit and 'thereby vapor- Referring vtothe accompanying drawing, a C4 hydrocarbon 'feed containing an unsaturatedhw dr'o'carbon, which itis desired to recover, enters absorber .I via 'line 2. Fur'fur'al is .continuously injectedintov the top of absorber I 'via' line 3. Ih'e iurfl'lral, enriched in unsaturated hydrocarbongiswithdrawn via line 4, The' overhead from 'coliirrin I lis condensedin f'condenser 5 'and fed to alilatr'wcret is allowed t0 Separateinto tivo layers, the lower layer being a water layer 'and the' upper layer being 'composed Yof :residual C4 hydrocarbons. -A portion of 'the V'upper vlayer is Lfed as reflux via 'li-ne '-'i to the 4top l`o' `column I entering 'fait Aa point slightly 'above the point ci Vfurfural entry. The balance of the hydrocarbon layer 'is withdrawn via line 8.

`he rich iurfural is ie'd via line 4 5to stripper @l 'where the unsaturated hydrocarbon dissolved therein is ldri-ven oir in v'the usual way,- Athe lean fur'fural being withdrawn vialine If. The overhead is condensed and the 'condensate accumul lated in tank II where it visa-llowed to-separate into two layers. lThe upper hydrocarbon 4layer is, inparty fed as refluxvia `line I2 tothetop of column 9, while Ythe balance is withdriav'mas product rvia line I3.

The lean furfural passes via line Ii! through cooler |14 'where it is cooled to a Kpoint .suitable for reintroduction into thev absorber 'Il andis then recycled via lline I5 to surge tank i6 whence it is fedinto absorber I.

Aside stream ofthe cooled urfurall islpassed via line Il 'to the re-run unit which is constructed inthe manner described .in Fig'. 2 of Buell et al. 2,350,584. `The re-run unit comprises two evap orators I8 and I@ arranged in series followed by a stripper 26. The furfural is introducedtinto the rst evaporator, the residuev passing yintotthe second evaporator and the residueV from the second evaporator passing into the stripperZ. Live steam generated Ain vaporizer 2! is injected into the bottom of stripper'20. The'vaporsof fur-tural I and water leaving unit 20 are fed into the bottom of evaporator IAQ and the vaporized furfural and water leaving unit i9 are fed into the bottom of evaporator I-, The vapors of the puriedfur fural Yand water pass voverhead. from evaporator I8 via line 2-2, are condensed in condenser 23 and accumulated in separator 2d where layer formation takes place. I-he polymer in admixture'with water andsufcient furfural to render it fluid is removed from the stripper-20 and discarded. The purified furiural layer accumulated irl-separator 24 is withdrawn and passed via line 25 into admixture with the main recycle stream rgoing to surge' or storage I6 In accordance with the present invention, the water layers separating in accumulators 6 and I I are withdrawn via lines 26 and 21, merged and passed via line 28- as the water used to generate process steam yfor the re-run unit in steam generator 2|.

Further, in accordance with the present invention, the Water lay'er separating in unit 24 is passed via line 29 to water surge 30 and thence as make-up water to the furfural recycle passed to absorber I.

If desired, a, portion of the-corrosive water new ing in line 28 may be passed via line Si and `injected directly in liquid form ,into the bottom of evaporator I9. A portion of this corrosive water might also be injected directly Vin liquid form into the bottom ofk evaporator i3, although this would almost never be found desirable. In very `rare instances all of the water in line 28 might be passed via lin'e 'SI tobe injected into the bottom of evaporator I9, in which case `a separate source of water would have to be provided for making process steam for the re-run unit in steam generator 2l.

Example In the manufacture of butadiene by two-stage dehydrogenation of normal butano, an absorber and Stripper were used between the first and second stage for separating butene-2 from normal butane and another absorber and stripper were employed to separate butadiene and butene-2 from a C4 `fraction of the second stage eflluent. The system was as shown in the drawingexcept that there were two absorber-stripper con-rbinations. Furfural was fed continuouslyfint'othe absorbers at 'the rate of 260,000 gal-Jhr. entering both absorbers. The furfural containing 5% of water by weight based on the weight of furfural and Water. Stripped furfural from both strippers was cooled to 1Z0-130 F. and the major part of the cooled product was passed via line l5 to furfural surge I6. The total volume of furfural in the entire system was 225,000 gal. Furfural was passed to the re-run unitat the rate of 3500 gal/hr.

Water appeared as a separate phase in the condensate accumulators provided for the overhead products of the absorbers and strippers at an average rate of 200 gaL/hr. This water was, in accordance with the present invention, withdrawn and passed at an average rate of 200 gaL/hr. via line 28 to steam generator 2| associated with vthe re-run unit. In the unit 2| this Water was vaporized and the resulting vapors employed as process steam in the re-run unit in the manner shown in the drawing.

The overhead from evaporator i8, composed of purified furfural vapors and steam free from corrosive substances, was fed via line 22 to condenser 23 where it was totally condensed. The condensate was passed to separator 24 and allowed to separate into two layers therein. The puried furfural layer was withdrawn via line 25 and fed to the furfural surge l E. The water layer appearing in unit 24 was composed of essentially pure water saturated with furfural and was withdrawn via line 29 and employed as make-up Water for the lean furfural fed to the absorbers. At times the amount of water from this source Was insufficient and it was necessary to add small amounts of water from another source.

By operating in accordance with this example, corrosion in the extractive distillation systems was greatly reduced. Furthermore, diieulty which had previously been encountered due to fouling of the tubes in steam generator 2l was eliminated.

The process of the present invention gives rise to numerous advantages over prior practice. Among these the following may be enumerated: the principal advantage of the present invention is that the corrosive material is removed from the water going overhead in the absorbers and strippers before this water is returned to the main system. Another advantage is that the Water used for making process steam contains less furfural and therefore fouling of the tubes in the steam generating unit is prevented. Another advantage is that the Water used for making process steam contains less furfural than was -the case where the prior method of using the Water layer derived from the re-run overhead was employed as the source of water; therefore the furfural is stripped from the polymers faster in the re-run unit and less furfural is polymerized in this part of the process. Another advantage is vthat less furfural is polymerized in the steam generating unit. Another advantage is that less steam is required for stripping furfural from the polymers in the re-run unit. Another advantage is that the process of the present invention is carried out in a simple and economical manner and that no additional equipment is required to adopt the process of the present invention to existing plants, the only change required is a change in the piping layout of the plant. Many other advantages of the present invention will be apparent to those skilled in the art in the light of this disclosure.

I claim: 4

1. In a process for the recovery of unsaturated hydrocarbons from admixture with less saturated hydrocarbons by extractive distillation with furfural containing dissolved Water as selective solvent wherein water is volatilized and passes overhead together With hydrocarbonsfrom furfural absorbing and furfural stripping steps, the total overhead from each of said steps is condensed and is separated into two layers, namely, a hydrocarbon layer and an aqueous layer` containing corrosive impurities; while a portion of stripped furfural is withdrawn from said furfural stripping step and such withdrawn furfural is steam distilled to remove polymers and other impurities therefrom prior to returning said furfural to said furfural absorption step; that improvement which comprises eliminating corrosive impurities by withdrawing said aqueous layers containing corrosive impurities and using them as the source of steam for steam distilling said stripped furfural.

2. In a process for the recovery of unsaturated hydrocarbons from admixture with less saturated hydrocarbons by extractive distillation with furfural containing dissolved Water as selective solvent wherein Water is volatilized and passes overhead together with hydrocarbons from furfural absorbing and furfural stripping steps, the total overhead from each? of said steps is condensed and is separated into two layers, namely, a hydrocarbon layer and an aqueous layer containing corrosive impurities; while a portion of stripped furfural is withdrawn from said furfural stripping step and such withdrawn furfural is steam distilled to remove polymers and other impurities therefrom prior to returning said furfural to said furfural absorption step; that improvement which comprises eliminating corrosive impurities and decreasing loss of water and furfural from the system by withdrawing said aqueous layers containing corrosive impurities, employing them as the source of steam for steam distilling said stripped furfural, and returning the water distilled overhead with such furfural to the extractive distillation system.

3. In a process for the recovery of unsaturated hydrocarbons from admixture with less saturated hydrocarbons by extractive distillation with furfural containing dissolved water as selective solvent wherein water is volatilized and passes overhead together with hydrocarbons from furfural absorbing and furfural stripping steps, the total overhead from each of said steps is condensed and is separated into two layers, namely, a hydrocarbon layer and an aqueous layer containing corrosive impurities; while a portion of stripped furfural is withdrawn from said furfural stripping step and such withdrawn furfural is steam distilled to remove polymers and other impurities therefrom prior to returning said furfural to said furfural absorption step; that improvement which comprises eliminating corrosive impurities and decreasing loss of water and furfural from the system b y withdrawing said aqueous layers containing corrosive impurities, employing them as the source of steam for steam distilling said stripped furfural, condensing overhead steam and furfural vapors from said steam distillation of furfural, separating the resulting condensate into aqueous and furfural layers and introducing said last-mentioned aqueous layer as make-up Water into furfural fed to said furfural extraction step.

4. In a process for the recovery of unsaturated hydrocarbons from admiXture with less saturated hydrocarbons by extractive distillation with furfural containing dissolved water as selective solvent wherein water is volatilized and passes anche?) overhead together; withV hydrocarbons from furfural. absorbing and: furfural stripping steps,v the total overhead from each of ,said stepsis* condensed andisseparated into two layers, namely, a hydrocarbon layer and an aqueous' layer containing corrosive impurities; while a portion ofi strippedfurfural. is withdrawn from said' furi'uralrstripping step and. such. withdrawn: funtural is steam. distilled.. to remove: polymers and other. impurities therefrom 'priori to returning said furfural to said furfural absorption step; that improvement which comprises withdrawing said aqueous layers containing corrosive impurities, introducing them in liquid phase into said withdrawn furfural undergoing steam distillation, and withdrawing a corrosive kettle product from said steam distillation of furfural.

5. In a process for the recovery of unsaturated hydrocarbons irom admixture with less saturated hydrocarbons by extractive distillation with furfural containing dissolved water as selective solvent wherein water is volatilized and passes overhead together with hydrocarbons from furfural absorbing and furfural stripping steps, the total overhead from each of said steps is condensed and is separated into two layers, namely, a hydrocarbon layer and an aqueous layer containing corrosive impurities; while a portion of stripped furfural is withdrawn from said furfural stripping step and such withdrawn furfural is steam distilled to remove polymers and other impurities therefrom prior to returning said furfural to said furfural absorption step; that improvement which comprises withdrawing said aqueous layers containing corrosive impurities, separating them by distillation into a distillate containing water and furfural free from corrosive impurities, and a corrosive kettle product; and introducing said distillate into the eX- tractive distillation system.

6. In a process for the recovery of unsaturated hydrocarbons from admiXture with less saturated hydrocarbons by extractive distillation with furfural containing dissolved water as selective solvent wherein water is volatilized and passes overhead together with hydrocarbons from furfural absorbing and furfural stripping steps, the

total overhead from each of said steps is condensed and is separated into two layers, namely, a hydrocarbon layer and an aqueous layer containing corrosive impurities; while a portion of stripped furfural is withdrawn from said furfural stripping step and such withdrawn furfural is steam distilled to remove polymers and other impurities therefrom prior to returning said furfural to said iurfural absorption step; that improvement which comprises withdrawing said aqueous layers containing corrosive impurities, separating them by distillation into a distillate containing water and furfural free from corrosive impurities and a corrosive kettle product; and introducing said distillate as make-up water'into furfural fed to said furfural absorption step in the extractive distillation system.,

7. In a process for the recovery of unsaturated hydrocarbons from admiXture with less saturated hydrocarbons by eXtra-ctive distillation with furfural containing dissolved water as selective solvent wherein water is volatilized and passes overhead together with hydrocarbons from fur- -tural absorbing and furfural stripping steps, the

total overhead from each of said steps is condensed and is separated into two layers, namely, a hydrocarbon layer and an aqueous layer containing corrosive impurities; while a portion of stripped furfurali's'withdrawn from said furfu'ral stripping step' and such withdrawn furfura-l is' passed to a rerun unit comprising a plurality of evaporators in seriesi followed by a stripper in which unit said' with'drawniiurfural is steaml dis'- till'ed to free it from' polymers and other impurities beforebei'ng recycled to4 s'ai'd furfural` absorbiing step, that improvement which'compri'ses'withe drawing said water layers containing corrosive impurities, introducing them in liquid phase into one of said evaporators in said rerun unit, withdrawing a kettle product containing corrosive impurities, condensing the water and fui-fura] distilled overhead in said rerun unit, separating the resulting condensate into aqueous and furfural layers, and introducing said last-named aqueous layer as make-up water into furfural fed to a furfural absorption step in the extractive distillation system.

8. In a process for the recovery of unsaturated hydrocarbons from admixture with less saturated hydrocarbons by extractive distillation with furfural containing dissolved water as selective solvent wherein water is volatilized and passes overhead together with hydrocarbons from furfural absorbing and furfural stripping steps, the total overhead from each of said steps is condensed and is separated into two layers, namely, a hydrocarbon layer and an aqueous layer containing corrosive impurities; while a portion of stripped furfural is withdrawn from said furfural stripping step and such withdrawn furiural is passed to a rerun unit comprising two evaporators in series followed by a stripper in which unit said withdrawn furfural is steam distilled to free it from polymers and other impurities before be- Y ing recycled to said furfural absorbing step, that improvement which comprises withdrawing said aqueous layers containing corrosive impurities, introducing them in liquid phase into the second of said evaporators, withdrawing a kettle product containing corrosive impurities, condensing the water and furfural distilled overhead in said rerun unit, separating the resulting condensate into aqueous and furfural layers, and introducing said last-named aqueous layer as make-up water into furfural fed to a furfural absorption step in the extractive distillation system.

9. In a process for the recovery of unsaturated hydrocarbons from admixture with less saturated hydrocarbons by extractive distillation with furfural containing dissolved water as selective solvent wherein water is volatilized and passes overhead together with hydrocarbons from furfural absorbing and furfural stripping steps, the total overhead from each of said steps is condensed and is separated into two layers, namely,

a hydrocarbon layer and an aqueous layer conf taining corrosive impurities; while a portion of stripped urfural is withdrawn from said furfural stripping step and such withdrawn furfural is passed to a rerun unit comprising two evaporators in series followed by a stripper in which rerun unit said withdrawn furfural is steam distilled to free it from polymers and other impurities before being recycled to said furfural absorbing step, that improvement which comprises withdrawing said aqueous layers containing corrosive impurities, vaporizing a part of said aqueous layers, withdrawing a kettle product containing corrosive impurities from such vaporivZation step, introducing steam resulting from such vaporization into said stripper of said rerun unit as the source of steam for said steam distilling unit, introducing another part of said aqueous 2,419,039 1 1 12 layers inliquid phase into the second of. said Y REFERENCES CITED evaporators,'condensing,Water and furfural distilled overhead in said rerun unit, separating mem llilswnferens are of record in th the resulting condensate into aqueous ,and furp fura] layers, and introducing said last named 5 UNITED STATES PATENTS aqueous layer as make-up Water into furfural Number Y Name, Date fed to a furfural absorption step in the eXtrac- 2,177 183 Kraft et al Oct." 24, 1939 tive dltluatlon System 2,350,584 Buen et a1 June s, 1944 2,350,609 Hachmuth June 6, 1944 VIRGIL SCARTH' ,10 2,366,360 Semon Jan. 2, 1945 Cla-www Certificate of Correction Patent No. 2,419,039. April 15, 1947.

VIRGIL SOARTH It is hereby certied that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 4, line 28, after the commeJ and before the Word removed insert 'is line 68, after re-run insert unfit; column 6, line 75, for containing read contained; and that the said Letters Patent should be read With these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 10th day of June, A. D. 1947.

[SEAL] LESLIE FRAZER,

First Assistant ommz'ssioner of Patents. 

